MX2501 Bluetooth pH & Temperature Datalogger

The HOBO MX2501 pH and Temperature Data Logger is designed for long-term monitoring of pH in estuaries, lakes, streams, rivers, and oceans. Leveraging Bluetooth Low Energy® (BLE) technology, the MX2501 pH Logger communicates wirelessly with the free HOBOConnect app making logger setup, calibration, and data offload quick and easy.

A guided pH calibration process on the HOBOConnect app makes an otherwise complicated process easier to follow. This affordable and compact logger dramatically cuts the time and effort needed to collect field data, while also offering higher resolution in data.

NOTE: pH electrodes should always be stored in storage solution when not deployed.

Highlighted Features:

  • Guided pH calibration following on-screen prompts in HOBOConnect app
  • Rugged PVC housing for deployment in both freshwater and saltwater environments
  • Quick and easy data offload via Bluetooth Low Energy (BLE) to iOS and Android devices
  • Water detection system for longer battery life and less maintenance
  • Potentiometric pH electrode with plastic body, gel electrolyte, and double cloth junction
  • User-replaceable battery, pH electrode, and anti-biofouling copper guard
  • Accuracy of ±0.10 pH units within ±10°C of temperature at calibration


Key Specifications:

pH Range 2.00 to 12.00 pH; -512 to 512 mV
pH Accuracy ±0.10 pH units within ±10°C of temperature at calibration; ±0.20 mV
pH Resolution 0.01 pH; 0.02 mV
pH Response Time 1 minute typical to 90% at constant temperature in stirred water
Temperature Range -2° to 50°C
Temperature Accuracy ±0.2°C
Temperature Resolution 0.04°C
Operating Range -2° to 50°C - non-freezing
Waterproof To 40 m
Wireless Data Standard Bluetooth Low Energy (Bluetooth Smart)
Transmission Range Approximately 30.5 m line-of-sight in air
Logging Rate 1 second to 18 hours
Battery Type One AA 1.5 Volt, user-replaceable
Battery Life 1 year typical at 25°C with logging interval of 1 minute and Bluetooth Always On selected in software.
2 years typical at 25°C with logging interval of 1 minute and Bluetooth Off Water Detect enabled in software.
3 years typical at 25°C with logging interval of 1 minute and Bluetooth Always Off selected in software.
pH Electrode Life 6 months
Memory 152 KB (43,300 measurements, maximum)
Dimensions 22.86 x 4.27 cm
Weight 268.2 g
Wetted Materials Logger: PVC housing and sensor end cap, polycarbonate closure caps and mounting end cap with a TPE switch
pH electrode: plastic-bodied with Pellon® junctions and gel electrolyte, glass pH sensor bulb


HOBOConnect App

Onset's free HOBOconnect app makes it fast and easy to configure compatible HOBO MX Series data loggers and manage the collected data. Just download the app from the Apple App Store or Google Play to your mobile device, or download from the Onset website to your Windows computer. With HOBOconnect, you can view data in graphs, check the operational status of loggers, share data files and graph images for analysis in Excel, Numbers, and other applications, plus store data in the cloud. HOBOconnect also lets you quickly set up audible alarm notifications, so you're immediately alerted to any problems.

  • Communicates to HOBO MX data loggers using Bluetooth (LE) technology
  • No internet connection required
  • Set data logger's name, password, logging rate, alarm threshold, start and stop time
  • Automatically upload data to Onset's cloud-based HOBOlink software to store and merge data files
  • Configure and clear audible alarms
  • Page the data logger
  • Quickly download and view data


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